Answer:
As the food moves through the gastrointestinal tract, and when it reaches the duodenum via the stomach, the food or the paste, that is, chyme becomes acidic because of the presence of acid in the stomach. When this acidic chyme moves towards the first section of the duodenum, it results in the discharging of cholecystokinin and secretin from the duodenal mucosa, which further instigates the pancreas to discharge alkaline pancreatic juice that comprises pancreatic enzymes and bicarbonate ions.
Now the bicarbonate ions will turn the chyme alkaline and is now known as chyle. It is made alkaline as the pancreatic enzyme needs alkaline pH to function on food. The intestinal juice is also secreted due to the discharging of similar hormones as mentioned above. However, the difference is that both the mechanical stimulus and nervous stimulus results in the discharging of intestinal juice, though it is not true for pancreatic juice.
Answer:
they bind to protein-coupled transmembrane receptors with higher complexity than those found in prokaryotes
Explanation:
G-proteins are proteins found inside the cells that function as molecular switches which are activated by binding to guanosine triphosphate (GTP), while they are inactive by binding to guanosine diphosphate (GDP). The G-proteins bind to G-protein-coupled transmembrane receptors (GPCRs) in the cytoplasmic region. The GPCRs are a very diverse group of proteins that are activated by extracellular molecules ranging from small peptides to large proteins, including pheromones, neurotransmitters, light-sensitive compounds, etc, thereby allowing them to respond to diverse stimuli from the extracellular environment. In consequence, it is reasonable to suppose that the signaling pathways in which G proteins are involved have a higher complexity level than those observed in primitive prokaryotic organisms.
